Because of the world-wide shortage of petroleum-based raw materials, it is imperative that recovery and recycle technology be developed to conserve the supply of petroleum and utilize dicarboxylic waste streams to the fullest advantage.
One of several such waste streams is a so-called bleed stream from adipic acid manufacture. Such a waste stream generally consists of:
______________________________________ HNO.sub.3 2-25% Succinic Acid 3-10% Glutaric Acid 8-35% Adipic Acid 3-8% Water Balance ______________________________________
The mother liquor from oxidation of various organic compounds, as described in Kuceski U.S. Pat. No. 2,824,122 may be used.
The art is well aware of the existence of such bleed streams which presently are burned or sewered to dispose of them. Such disposal is not only an economic burden but a source of pollution as well.
This waste stream is called a bleed stream by those in the adipic acid industry because it is a stream bled from the filtrate liquors from adipic acid purification procedures in order to remove contaminants which build up in the liquors.
Bleed streams formed in the nitric acid oxidation of cyclohexane, cyclohexanol and cyclohexanone and mixtures thereof, produce significant amounts of succinic acid and glutaric acid as byproducts with the desired adipic acid, as indicated in the foregoing table. The adipic acid is needed in high purity in order to make it feasible for use in making nylon. Therefore, contamination of it with other dibasic acids is undesirable. In the usual practice of obtaining maximum yields of adipic acid, adipic acid is crystallized from the oxidized reaction mixture and the filtrate is concentrated and then further crystallized to obtain additional amounts of adipic acid. This process is repeated until the adipic acid which is crystallized becomes impure because of co-crystallization of the byproduct succinic acid and glutaric acid which are present. Many times there is recycling of the filtrate to the first crystallization stage or other steps, but eventually the concentration of succinic acid and glutaric acid builds to such a high concentration that further concentration and crystallization yield only mixtures of other dibasic acids with the adipic acid. Before this point is reached, a portion of the filtrate is bled off and added to the stream from which adipic acid is crystallized. Hence, the name bleed stream.
This bleed stream is not a small factor in the United States today. The dibasic acids in bleed streams from adipic acid plants in the U.S. amount to as much as 200 million pounds per year. If nitric acid and water of solution are also included, the weight of the bleed stream amounts to as much as one billion pounds per year.
Therefore, the bleed streams which are formed are substantial in quantity and contain valuable dibasic acids which heretofore could not be utilized as such economically or realistically because of the great amount of nitric acid, and catalyst also in most plants, which remains with the dibasic acids in solution.
It is quite evident therefore, that if a use can be made for such a bleed stream, per se, not only economic values would be realized but an economic burden would be avoided because of the cost of disposal of a large amount of bleed stream.
One of the large requirements in the United States and foreign countries is for a series of polyamides which are useful as such or as intermediates in the manufacture of water-treating compounds, paper-retention aids, or as coatings, and as wet-strength resins for paper.